1. Field of the Invention
The present invention relates to apparatus and methods for use in the production of hydrocarbons. In another aspect, the present invention relates to apparatus and methods for examining gravel packs utilized in completed hydrocarbon wells. In even another aspect, the present invention relates to apparatus and methods for determining the quality of gravel packs utilized in completed hydrocarbon wells.
2. Description of the Related Art
Oil and gas wells are often completed in unconsolidated formations containing loose and incompetent fines and sand which migrate with fluids produced by the wells. The presence of formation fines and sand in the produced fluids is disadvantageous and undesirable in that the particles abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones in the wells.
Heretofore, unconsolidated subterranean zones have been stimulated by creating fractures in the zones and depositing particulate proppant material in the fractures to maintain them in open positions. In addition, the proppant has heretofore been consolidated within the fractures into hard permeable masses to reduce the potential of proppant flowback and migration of formation fines and sands through the fractures with produced fluids.
Thus, it is not hard to imagine that in the production of hydrocarbons from a subterranean formation penetrated by a wellbore, it is often necessary to address the problem of the production of fine particulate materials with the desired well fluids. Such fine particulate materials can cause abrasive wear on well components such as pumps, valves and tubular goods resulting in costly replacement. Additionally, these particulates must be separated from the desired well fluids before transport, processing or sale. Further, these particulate materials can accumulate in the wellbore and in the near wellbore area and greatly reduce or completely stop further production of the fluids of value.
Minimizing the production of particulate materials such as formation sand without reducing well productivity has long been the goal of sand control operations. Toward that goal, various technologies have been used including resin consolidation, gravel packing, overbalanced perforating with resin consolidation and the like.
For example, gravel packs which include sand screens and the like have commonly been installed in the wellbores penetrating unconsolidated zones. The gravel packs serve as filters and help to assure that fines and sand do not migrate with produced fluids into the wellbores.
In a typical gravel pack completion, a screen is placed in the wellbore and positioned within the unconsolidated subterranean zone that is to be completed. The screen is typically connected to a tool that includes a production packer and a cross-over, and the tool is, in turn, connected to a work or production string. A particulate material that is usually graded sand, often referred to in the art as gravel, is pumped in a slurry down the work or production string and through the cross-over whereby it flows into the annulus between the screen and the wellbore. The liquid forming the slurry leaks off into the subterranean zone and/or through the screen that is sized to prevent the sand in the slurry from flowing there-through. As a result, the sand is deposited in the annulus around the screen whereby it forms a gravel pack. The size of the sand in the gravel pack is selected such that it prevents formation fines and sand from flowing into the wellbore with produced fluids.
Gravel pack technology has its own set of problems and limitations. These include problems in assuring placement uniformity and efficiency. Often, if not utilized correctly, or under certain circumstances, gravel packs also have the undesired side effect of reducing well productivity.
Specifically, a problem which is often encountered in forming gravel packs, particularly gravel packs in long and/or deviated unconsolidated producing intervals, is the formation of sand bridges in the annulus. That is, non-uniform sand packing of the annulus between the screen and the wellbore often occurs as a result of the loss of carrier liquid from the sand slurry into high permeability portions of the subterranean zone which in turn causes the formation of sand bridges in the annulus before all the sand has been placed. The sand bridges block further flow of the slurry through the annulus which leaves voids below the bridges formed. When the well is placed on production, the flow of produced fluids is concentrated through the voids in the gravel pack which soon causes the screen to be eroded and the migration of fines and sand with the produced fluids to result.
It is well known, that to be effective, the gravel pack must comprise densely packed sand without voids or cavities in the sand. If portions of the annulus around the screen are not packed completely with sand, formation fluids containing formation sand will quickly erode the screen, leading to a gravel pack failure. Further, if the gravel pack initially is not densely packed, subsequent compaction caused by, for example, flow of the formation fluids, can result in voids and cavities within the gravel pack.
There has been much prior art relating to evaluation of gravel packs.
U.S. Pat. No. 4,423,323, issued Dec. 27, 1983 to Ellis, et al., discloses a neutron logging method and apparatus for determining a formation characteristic free of environmental effects. Specifically, a neutron logging tool is passed through the borehole while irradiating the formation with neutrons. Neutrons exiting the formation are detected with neutron detectors and count rate signals are generated. In response to these signals, an indication of porosity, substantially independent of error due to tool standoff from said borehole wall, is produced. In addition, values of tool standoff are also generated. These standoff values are then filtered to reduce statistical variations and are used to generate improved indications of porosity. A further aspect is the determination of tool standoff, effective cement/casing thickness, or gravel pack quality from the relation between the logarithms of the count rates and the empirically derived response curves without an explicit down-hole measurement.
U.S. Pat. No. 4,587,423, issued May 6, 1986 to Boyce, discloses a method for gravel pack evaluation utilizing a logging tool with a gamma source and gamma detector. Using a Monte Carlo modeling of gravel pack conditions in a completed borehole, a straightforward expression for the determination of percent packing as a function of known or measurable borehole quantities is derived, from which an accurate quantitative gravel pack log may be obtained for purposes of evaluating gravel pack quality.
U.S. Pat. No. 4,783,995 issued Nov. 15, 1988, to Michel et al., discloses an apparatus and method for logging the density of a gravel pack installation in a drill hole while the gravel pack installation tool is being withdrawn from the drill hole. After the apparatus is recovered at the earth""s surface, the density log is recovered by means of a dedicated surface readout module. The logged data of the density of the gravel packed zone is examined for voids in the gravel pack. If any such void is indicated from the data, remedial action can be taken promptly while the gravel pack equipment is still at the drill hole site.
U.S. Pat. No. 4,950,892, issued to Olesen, discloses a method and tool for investigating a gravel pack located in the annulus between the tubing/screen and the casing of a borehole. The method includes moving a logging tool through the tubing/screen over the depth region of the gravel pack. The logging tool includes a neutron source able to emit neutrons at such an energy that their interaction with a first set of atoms indicative of the gravel pack quality causes the production of gamma-rays, and at least one gamma-ray detector. The method also includes deriving a measurement of the number of gamma-rays resulting from the interaction of said neutrons and said first set of atoms of the gravel pack material, and that are detected by said detector over a predetermined counting time interval.
Olesen notes that prior investigations have indicated the applicability of wireline logging techniques to the evaluation of gravel packs, and makes reference to xe2x80x9cGravel Pack Evaluationxe2x80x9d, by M. R. Neal, first presented (Paper SPE 11232) at the 57th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME, New Orleans, La., September, 1982, published in the Journal of Petroleum Technology, September, 1983, pp. 1611-1616. Olesen notes the paper describes the responses of three well logging tools, the compensated neutron tool (neutron source and two neutron detectors), the nuclear fluid density-meter tool (gamma-ray source and one gamma-ray detector), and the dual-spacing gamma-ray tool (gamma-ray source and two gamma-ray detectors), to various gravel pack situations and showed that each tool responded well to changes in density of the material in the annulus between the screen (of the gravel pack hardware) and the casing. Olesen finally notes that although Neal""s work provided useful qualitative information concerning gravel pack quality, it did not provide a procedure by which a quantitative evaluation could be made.
Olesen makes further reference to research by M. R. Neal and J. F. Carroll, as reported in a paper entitled xe2x80x9cA Quantitative Approach to Gravel Pack Evaluationxe2x80x9d, 6th SPE of AIME Formation Damage Symposium, Bakersfield, Calif., Feb. 13-14, 1984. Olesen notes this paper as demonstrating that tool response (count rate) could be directly related to the percent void space in the gravel pack, and led to the development of interpretive procedures for determining percent packing when field hardware is the same as that used for laboratory calibration measurements and for making a quick-look quantitative approximation when the well hardware differs from laboratory hardware.
U.S. Pat. No. 5,481,105, issued Jan. 2, 1996 to Gold, discloses an apparatus (sonde) and method of measuring density, or gravel pack quality, in a cased well borehole using a fast neutron source and one or more thermal neutron detectors is described. In one embodiment, a neutron source creates a fast neutron flux which reacts primarily with the material within the borehole casing while a collocated neutron detector counts the number of backscattered thermal neutrons. A novel means of obtaining azimuthal measurement discrimination is provided by a rotating neutron shield. In one instance the shield is quite substantial, creating a narrow measurement window. In another instance, the shield only marginally screens the detector, creating a large measurement window. In an alternative embodiment, a second thermal neutron detector is spaced distally from the neutron source and first detector. This second detector is used to provide a measurement of the borehole""s background, or environmental neutron activity, and can be used to improve the quality of the sonde""s gravel pack density measurement.
Gold further teaches it is possible to locate a void in the gravel with a tool that is responsive to density, and provides, as an example, a density-measuring device where there is a substantial contrast between the fluid in the pores and the gravel. Gold then notes that density measurement with a typical gamma-ray fluid density tool is made all the more difficult as a result of recent advances that have been introduced for gravel pack materials. Gold further explains that the contrast in the density of the matrix and fluid has been reduced with the advent of new packing materials, and teaches away from use of a gamma-ray density tool by commenting that xe2x80x9cthe loss in contrast in the density measurement between the matrix material and the pore fluid makes measurement the gamma density approach difficult, perhaps almost impossible.xe2x80x9d
Although not directed for use in evaluation of gravel packs, U.S. Pat. No. 5,841,135, issued Nov. 24, 1998, to Stoller et al., discloses a method and apparatus for measuring formation density and the formation photo-electric factor with a multi-detector gamma-gamma tool. Specifically, Stoller et al. disclose a method and tool for determining formation density by using an array of gamma-ray detectors. In this invention, the collimated detectors have varying depths of investigation into the formation. At small standoffs a short-spaced (SS) detector investigates mainly the mud and mudcake and a shallow layer of the formation. Unlike the SS, a mid-spaced (MS) detector has a deeper depth of investigation and is sensitive to the borehole and the formation even at increased standoffs. A long-spaced (LS) detector is mainly sensitive to the formation density and its density reading is corrected by using the standoff information from the MS and SS detectors. In addition to measuring density, this invention can measure the photo-electric factor (PEF) of the formation. Because photo-electric absorption preferentially removes low-energy gamma-rays, the tool housing needs to allow passage of low-energy gamma-rays. This can be accomplished through the use of a window of a material with a low atomic number (Z) or through the use of a low-Z housing material like titanium. Typical window materials are beryllium and titanium. Housing materials can be titanium or for lower pressure requirements graphite or high-strength carbon compounds.
However, in spite of the above advancements, there still exists a need in the art for apparatus and methods for determining gravel pack density, quality or uniformity.
There is another need in the art for apparatus and methods for determining gravel pack density, quality or uniformity, which do not suffer from the disadvantages of the prior art apparatus and methods.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.
It is an object of the present invention to provide for apparatus and methods for determining gravel pack density, quality or uniformity.
It is another object of the present invention to provide for apparatus and methods for determining gravel pack density, quality or uniformity, which do not suffer from the disadvantages of the prior art apparatus and methods.
It is even another object of the present invention to provide for apparatus and methods which improve on the prior art gamma density approaches limited by the loss in contrast in the density measurement between the matrix material and the pore fluid.
These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.
According to one embodiment of the present invention, there is provided an apparatus for use in a completed well borehole, for evaluating a gravel pack positioned in a wellbore. The apparatus generally includes a housing suitable for positioning in the completed wellbore. The apparatus also includes a radiation source for providing radiation to the gravel pack. The apparatus even also includes a radiation detector attached to the housing, wherein the detector is suitable to provide azimuthal resolution of radiation from the gravel pack.
According to another embodiment of the present invention, there is provided an apparatus for use in a completed well borehole, for evaluating a gravel pack positioned in a wellbore. The apparatus generally includes a housing suitable for positioning in the completed wellbore. The apparatus also includes a radiation source attached to the housing, wherein the source is suitable to provide irradiation to azimuthally resolve the gravel pack. Finally, the apparatus also includes a radiation detector for detecting radiation from the gravel pack.
According to even another embodiment of the present invention, these is provided an apparatus for use in a completed well borehole, for evaluating a gravel pack positioned in the wellbore. The apparatus includes a housing suitable for positioning in the completed wellbore. The apparatus also includes a radiation source for providing radiation to the gravel pack. The apparatus further includes n radiation detectors attached to the housing in a plane perpendicular to a longitudinal axis of the housing, wherein n detectors are suitable to provide azimuthal resolution of radiation from the gravel pack.
According to still another embodiment of the present invention, there is provided a method for evaluating a gravel pack positioned in the completed wellbore, the wellbore having a longitudinal axis. The method includes azimuthally scanning the gravel pack for radiation, wherein during said scanning, radiation is detected from an angular arc of the gravel pack between 1xc2x0 and 359xc2x0 at any one time.
According to yet another embodiment of the present invention, there is provided a method for evaluating a wellbore gravel pack positioned in a completed wellbore. The method includes positioning in the wellbore, a tool having a longitudinal axis, and the tool comprising n detectors positioned in a plane perpendicular to the longitudinal axis, wherein n is at least 1, and each detector is suitable for detecting radiation from an angular arc of the gravel pack, wherein the angular arc for each detector is independently selected to be between 1xc2x0 and 359xc2x0 at any one time. The method also includes detecting radiation with the detectors while moving the tool longitudinally through the well bore.
In more specific embodiments of the above embodiments, the radiation detector is collimated to preferentially receive radiation from an angular arc of the gravel pack of between 1xc2x0 and 359xc2x0 at any one time.
In an even more specific embodiment of the above embodiments, the radiation detector is collimated to preferentially receive radiation from an angular arc of the gravel pack of between 1xc2x0 and xcex1 or between 1 and (360xc2x0xe2x88x92xcex1), wherein xcex1 is in the range of about 25xc2x0 to about 155xc2x0. More specifically, the detector may comprise n detectors positioned in a plane perpendicular to the longitudinal housing axis, wherein n is at least 2, and wherein each detector is suitable to receive radiation from an angular arc of the gravel pack of between 1xc2x0 and 359xc2x0 at any one time, with or without overlap between the detectors.
These and other embodiments of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.